The lifetime of excited fluorescent or luminescent dyes, or of an intrinsic autofluorescent response to an excitation light, is highly sensitive and selective to chemical and/or biological properties of the surrounding environment of the dyes or autofluorescent material in the sample. Images of the fluorescence/luminescence lifetime can be used for understanding these chemical or biological properties. Time-correlated single-photon counting (TCSPC) or frequency-domain phase measurement can be used for obtaining the images. In particular, TCSPC is a histogram-based method that uses ultra-fast laser pulse with sub-nanosecond resolution for fluorescence/luminescence excitation and obtains the fluorescent lifetime image through image reconstruction. The frequency-domain phase measurement uses a laser diode or a low-power LED as an excitation source.